Police and anti-capitalism protesters clashed in ugly scenes in Melbourne after a group was evicted from their CBD camp.

The scuffles spilled into city streets after officers forcibly removed Occupy Melbourne demonstrators from the City Square on Friday morning, dragging many writhing and kicking and carrying others.

Police denied using excessive force to break up the protests, which blocked major city intersections and public transport for most of the day.

Up to 20 people were arrested and could face charges such as trespass, resisting arrest and hindering police, but police said a number of protesters were removed and later released.

More than 20 protesters had minor injuries, with one taken to hospital, while two officers were also injured, one of whom was taken to hospital to have his eye flushed.

One protester claimed a 14-year-old boy was trampled by a horse and then sprayed with capsicum spray.

Another protester, Thomas Tymms, said police kneed him in the face, giving him a bloody nose and black eye in actions he described as "outrageous".

"This is what needs to happen for people to stand up and wake up. We don't really live in a democracy, we live in a place ruled by the rich and police protect the rich," he said. But Assistant Commissioner Stephen Fontana denied police used excessive force.

"We don't really want to engage in this sort of activity but we're not going to back down either," Mr Fontana told reporters.

He said police boosted numbers from 150 to more than 400, in line with the increase in protesters.

"We will continue to keep moving through until we have cleared the streets," he said.

"We're trying to use the minimum amount of force as possible.

"They've had more than ample time to make their point in terms of what their protest is about and I think it's time to give the City Square back to the citizens of Melbourne."

He said police were resourced to deal with any future protests if it continued into the weekend.

The chaos was sparked after about 100 Occupy Melbourne demonstrators, who had camped out in the City Square for a week as part of global protests against corporate greed, defied an order to leave by 9am.

By about 12.30pm, a huge police contingent, including the riot squad, began dragging protesters out of the square and cleared the area within 10 minutes.

As the protesters were moved on, more joined in, blocking trams and the busy intersection of Swanston and Collins streets before being pushed further down Swanston Street. Mounted police, riot police and the dog squad controlled the scene.

Melbourne Lord Mayor Robert Doyle has said a week was long enough to occupy the centre of the city. Mr Doyle said the site would remain fenced for about 48 hours while it was cleaned up and any damage fixed.

The protest moved down Swanston Street towards Trades Hall, where protesters were on Friday night deciding on their next move.